An estimated 700,000 people in the United States are infected with HIV. Effective treatment of HIV infection requires prolonged administration of multiple antiretroviral agents. Incorporating clinical pharmacology expertise into the design, performance, and analysis of HIV clinical trials is therefore essential. Establishment of a main AIDS Clinic Trial Unit (ACTU) at Vanderbilt University would bring extensive expertise in clinical pharmacology to the AIDS Clinic Trials Group (ACTG). Vanderbilt ACTU investigators will participate in several studies including: inter-individual variability in response to antiretroviral therapy; drug disposition and metabolism; drug-drug interactions; tissue delivery of protease inhibitors and other drugs by membrane transporters (including P-glycoprotein); and the application of ultra-intensive CSF sampling approaches to study HIV treatment and pathogenesis in the CNS. The investigators also may apply advanced mass spectroscopy techniques to HIV clinical trials. The use of state-of-the-art clinical pharmacology strategies to HIV clinical trials may ultimately improve treatment of HIV infection and its complications, and allow therapy to be appropriately individualized. Vanderbilt University investigators also will contribute expertise to other innovative HIV-related laboratory efforts. These include: developing novel antiretroviral therapeutics; studying HIV-1 virion assembly and HIV-1 accessory proteins; developing novel HIV-related assays; understanding viral pathogenesis of AIDS-related malignancies; characterizing host-pathogen interactions in the gastrointestinal tract during AIDS; and developing strategies to optimize the design of antiretroviral agents and AIDS vaccines. The Principal Investigator leads an established HIV clinical trials program at Vanderbilt University, and the proposed ACTU incorporates a large Vanderbilt- affiliated HIV primary care clinic. Technically demanding studies will be facilitated by the Vanderbilt University General Clinical Research Center (GCRC). The proposed ACTU will not only enroll patients into ACTG clinical trials, but will provide the ACTG the ability to address important questions concerning AIDS treatment and pathogenesis.